FIGURE 4.

Heterosynaptic depression depends on GABA_BRs in both the dorsal and the ventral hippocampus. Time courses of tHSD induced under normal conditions (open symbols) or blockade of GABA_BRs by their selective antagonists CGP 52432 (10 μM) or CGP 46381 (50 μM) (filled symbols), in the dorsal and the ventral hippocampus. Three intensities of CS, weak (A), moderate (B), or strong (C) were used to induce tHSD. Numbers into parenthesis indicate the number of slices used. Insets are examples of fEPSP recordings for an inter-stimulus interval of 200 ms; a 150 ms-long interval between conditioning and test response is omitted for clarity reasons. Traces in black denote control responses of the conditioned path. Calibration bars: 1 mV, 10 ms. Artifacts are truncated. Note that blockade of GABA_BRs by CGP eliminates tHSD induced by weak CS, in both hippocampal segments, and tHSD induced by moderate CS in the ventral hippocampus. However, significant tHSD induced by moderate CS under blockade of GABA_BRs remained in the dorsal hippocampus, at 50−100 ms. Also, significant tHSD induced by strong CS under blockade of GABA_BRs remained in the dorsal (50−200 ms) and the ventral hippocampus (50−100 ms).